This invention relates to electric heating and, more specifically, to an improved heater band and a method for making the band.
Heater bands are known for heating a container, as for example an extruder barrel containing a plastic melt or a water heater. Such a heater band is disclosed in Browne U.S. Pat. No. 2,976,387, owned by the assignee of the present invention. The heater band includes a heating element carried by and electrically insulated from a cover and a base, both of thin sheet metal. The base includes tabs or flanges which are folded over the cover to retain the electric heating element between the cover and the base. The sheet metal is of low mass, and when the underside of the base is in intimate contact with the container to be heated, satisfactory heat transfer from the heater band to the container takes place.
Two related problems arise with the heater band described above. First, if the band separates from the barrel creating a space therebetween, the heat transfer from the heating element to the container is reduced and the heating element becomes overheated since the sheet metal cannot sufficiently and adequately absorb the additional heat which was not dissipated as a result of inefficient heat transfer between the heating element and the container. This reduces the operational life of the heating element. Second, the wattage of the heating element must be selected to be less than the maximum possible wattage to assure that the heating element does not burn out if the band separates from the container.